1. Field of the Invention
The present invention relates to a flat display panel for displaying pictures such as characters and figures by utilizing a DC gas-discharge and a method of driving the same and is more particularly directed to the construction of a flat display panel of the electron-acceleration type with an internal memory function and a method of driving such a panel.
2. Description of the Prior Art
Prior-art plain gas-discharge indicator elements, with a gas-discharge tube constituting an element as shown in FIG. 1A consists of a gas-discharge tube 1 which is a discharge cell having an anode A and a cathode K, a resistor R connected to the anode A to control the discharge current, a DC voltage source 2 the positive pole of which is connected to the anode A through the resistor R and a voltage source 3 connected in series with the resistor R and the negative pole is connected to the cathode K through a voltage source 4.
The relationship between the DC discharge voltage V and the luminance B in such a gas discharge cell is shown in FIG. 1B wherein V.sub.B is the breakdown voltage, V.sub.M the discharge maintenance voltage and V.sub.E the discharge extinction voltage. It is apparent from this characteristic curve that a discharge occurs when the DC voltage V of power source 2 is increased to V.sub.B (breakdown voltage), and consequently, the luminance is B.sub.1 as shown in FIG. 1B. A discharge, once started, continues even if the applied voltage V is lowered below V.sub.B and it is extinguished only when the applied voltage is lowered to V.sub.E (extinction voltage), where the lowest luminance B.sub.2 is obtained. That is, there is a potential difference between the discharge breakdown voltage V.sub.B and the extinction voltage V.sub.E. Therefore, the applied DC voltage is the maintenance voltage V.sub.M, and a bi-stable state is provided; the discharge state is shown by point P' in FIG. 1B and the non-discharge state is shown by point P in FIG. 1B, to constitute a memory function.
For example, the voltage V.sub.M of the power source 2 is determined suitably according to the condition V.sub.E &lt; V.sub.M &lt; V.sub.B, and the voltage V.sub.M /2 and the voltage -V.sub.M /2 are respectively applied to the anode A and the cathode K at all times. Further, if the voltage (V.sub.B - V.sub.M)/2 of the voltage source 3 is superimposed on the anode A and the voltage -(V.sub.B -V.sub.M)/2 of the voltage source 4 is superimposed on the cathode K the applied potential difference between the anode A and the cathode K is the breakdown voltage V.sub.B ; therefore the discharge builds-up. On the contrary, the discharge can be extinguished by using a voltage satisfying the condition -(V.sub.M - V.sub.E)/2 for the anode A and using a voltage satisfying the condition (V.sub.M -V.sub.E)/2 for the cathode K.
Thus, in the conventional display device, the discharge cell 1 has a memory function by using the resistor R connected in series with the anode A to control the discharge current. Also, the flat discharge panel having a memory function is comprised of the discharge display element of the matrix type as shown in FIG. 1C, the discharge display element comprising the resistor R and the discharge cell 1.
However, the conventional discharge panel gives rise to drawbacks as summarized below.
1. The resistor R which is an essential requirement for the gas-discharge display element must have a value at which the tolerances are lower than 10% in order to realize higher reliability, higher luminance and higher stability of the display panel. However, it is very difficult to realize the tolerance with present-day techniques.
2. The time constant .tau. determined by the resistance of the resistor R and the capacitance of the stray condenser is too large to enable a quick response, because the resistor R (the resistance of the resistor R is from several hundred kilo ohms to about several mega ohms) is connected to the anode A of the discharge cell 1. Therefore, it is impossible to realize the high speed drive required to display the video signals. For example, in present-day devices, the turn-on time is from about several tens of microseconds to about several hundreds of microseconds in spite of the fact that the required time is lower than 9 microseconds.
3. In order to obtain light for the display in vacuum, ultraviolet radiation is generated by a negative glow function to excite phosphor material. Further, the visible light generated by the gas-discharge is used to obtain high intensity light. This results in a lower luminous efficiency and lower luminance than those of the present invention.
4. As will be seen from the above description, as the discharge cell is driven by the voltage amplitude, the conventional display panel does not realize a high quality picture. Because, the luminance changes according to the each state of the addressed state, the holding state and/or the half-selected state of the discharge cell, that is, each state of the discharge cell depends upon the input voltage.